1. Field of the Invention
The present invention pertains generally to agronomic mulch sheets for covering an area of soil or earth to aid in the retention of moisture and heat therein. More particularly, the present invention relates to such agronomic mulch sheets adapted to control or suppress the growth of vegetation in an area of ground upon which the sheet is placed, which control and suppression is derived from a design combining features of selective light transmittance and air permeability.
2. Description of the Prior Art
It is known in the prior art to cover agricultural or tillage areas with, for example, a plastic film for various and diverse purposes. Accordingly, differing varieties of mulch sheets have been employed in connection with the growing of fruits and vegetables, and coffee and cocoa beans. Without limitation, the advantages which may be realized include earlier harvesting, higher surface yields, suppression of weeds and other undesirable growth, higher ground temperature beneath the mulch, higher ground moisture with regular irrigation, lower irrigation requirements, and the prevention or reduction of erosion by wind and rain. Concomitantly, there are known disadvantages such as, for example, the difficulty of supplying irrigating water to the ground which results in a depletion of retained moisture whereby the soil gradually dries out, accumulation of heat under the film, exclusion of air, collection of gases which originate from fermentation in the ground or which are given off by various organic fertilizers (e.g., manure) and which, at higher temperatures, adversely affect plant growth and maturation. No conventional or commercially available agronomic mulch sheet currently exists to maximize the advantages of its use while simultaneously minimizing the drawbacks, or one which even balances these competing interests in a successful manner.
Numerous approaches have been taken in an attempt to achieve this desirable result. For example, various known mulch sheets have been formed with flap-like incisions in the sheet through which rain water or irrigating water may pass into the ground. However, it has been found in practice that after a relatively short amount of time weeds or other undesirable vegetation may grow through these incisions which, actually, magnifies the problem sought to be prevented since weed control is then further complicated by the presence of the mulch sheet. Additionally, the prior art mulch sheets have failed to recognize the importance of proper dimensioning of both the flap-like incisions and spacings therebetween. Thus, such sheets, typically fabricated with rather large dimensions of both the incision and distance between adjacent incisions, fail to insure sufficient exchange of gas between the ground and the surrounding air and, likewise, fail to prevent local accumulations of heat. Note, for example, the U.S. Pat. Nos. 3,805,446, 3,580,196, and 3,559,599. Other exemplary references will be found among those cited against U.S. Pat. No. 3,975,859 assigned to the assignee herein, which patent is incorporated herein by reference and relied upon. Similar problems have obtained with perforated films having incisions on the order of 10 mm, typical for use in film tunnels.
Additionally, the prior art recognizes such mulching films formed of plastic to which is added pigmentation (e.g., black pigment). Notwithstanding the use of such mulching sheets, the prior art has failed to recognize that the control or suppression of the growth of vegetation may be effectively achieved by proper control of the degree of pigmentation. Accordingly, typically-available black mulching sheets have been found to absorb a great amount of heat, thus providing very high temperatures locally beneath the film but fostering significantly lower ground temperatures beyond the fairly small local zone. Consequently, these mulch sheets are ineffective for selective control.
Nowhere does the prior art recognize the combined consideration of light transmittance and air permeability. Therefore, the need exists to provide an agronomic mulching sheet which properly balances all of the foregoing considerations and, thus, may be utilized to curb the growth of undesirable weeds or other vegetation in an efficient, simple, and economic manner.